Amphibian malformations and inbreeding

Inbreeding may lead to morphological malformations in a wide variety of taxa. We used genetic markers to evaluate whether malformed urodeles were more inbred and/or had less genetic diversity than normal salamanders. We captured 687 adult and 1259 larval tiger salamanders ( Ambystoma tigrinum tigrinum ), assessed each individual for gross malformations, and surveyed genetic variation among malformed and normal individuals using both cytoplasmic and nuclear markers. The most common malformations in both adults and larvae were brachydactyly, ectrodactyly and polyphalangy. The overall frequency of adults with malformations was 0.078 compared to 0.081 in larval samples. Genetic diversity was high in both normal and malformed salamanders, and there were no significant difference in measures of inbreeding ( f and F ), allele frequencies, mean individual heterozygosity or mean internal relatedness. Environmental contaminants or other extrinsic factors may lead to genome alternations that ultimately cause malformations, but our data indicate that inbreeding is not a causal mechanism.

Effects of pH on embryo tolerance and adult behavior in the tiger salamander, Ambystoma tigrinum tigrinum

We examined adult discrimination ability and embryo performance under different pH conditions in the eastern tiger salamander, Ambystoma tigrinum tigrinum. We collected individuals from three populations in habitats that differed naturally in pH, thus allowing interpretation of population-specific responses in embryos and adults. We conducted pool-choice experiments in the field using two pH treatments to determine adult pH discrimination ability and controlled laboratory toxicity tests using eight pH treatments to evaluate embryo performance. Adult discrimination ability differed among source populations. Male salamanders from the locality with the highest pH were more likely to stay in neutral-pH pools and more likely to leave acidic ones. Males from the locality with the lowest pH were also more likely to remain within neutral pools, but their rates of staying and leaving acidic ones did not differ. These results suggest that the pH of the source-population habitat may influence breeding-habitat discrimination by adults. Decreasing pH produced similar patterns of lethal (survival) and sublethal (date and size at hatching) effects on embryos from the three populations, with reduced performance at low pH. Survival of embryos was more than 70% at pH 4.5 and above, but decreased dramatically at lower pH levels. The pH at which 50% mortality occurs (LC50) was estimated as 4.2, suggesting that tiger salamanders from our populations were relatively acid tolerant compared with congeners. However, significant sublethal effects could reduce the subsequent success of surviving hatchlings. Our results are consistent with the hypothesis that adult discrimination ability depends on pH levels in the breeding habitat. This suggests that adult behavior patterns could influence the success of population reintroductions to previously acidified areas. Thus, data on pH responses at all stages in the amphibian life cycle should contribute to management decisions.

Sibling cannibalism in noncannibal morph Ambystoma tigrinum larvae and its correlation with high growth rates and early metamorphosis

We describe here, for the first time, the existence of an Ambystoma tigrinum tigrinum larval morph characterized by fast growth rates and early metamorphosis and triggered by cannibalism. This new morph does not have the anatomical specializations of true A. tigrinum cannibal morphs, i.e., enlarged vomerine teeth and a wider head described previously by several workers. Functionally, however, this new morph and true cannibal morphs achieve the same end; high growth rates and early metamorphosis may facilitate survival in individuals inhabiting temporary and unpredictable wetlands.